1. Field of the Invention
The present invention relates to steel strips for cans, and especially three-piece can bodies wherein the can bodies are produced by slitting can body blanks from steel strips having stripe-like multi-layer organic laminated films continuous in the length direction of the steel strips, followed by rolling and welding the can body blanks. The present invention also relates to a method of producing the steel strips for three-piece can bodies, and further, relates to resistance seam welded three-piece can bodies having a multi-layer organic film on the surface thereof.
2. Description of the Related Art
Seen from the viewpoint of the can manufacturing process, cans can be broadly classified into two types, normally a two-piece can where the can bottom and the can body are formed as an integral part and a can lid is fitted onto this part, typical examples of such can being DI can bodies (i.e., drawn and ironed can bodies) manufactured by a drawing.cndot.ironing process and DrD cans (i.e., drawn and redrawn can bodies) manufactured by a drawing process. The other type is a three-piece can, where a can bottom and a can top are fitted onto a body part, and typical cans of this type include soldered cans, bonded cans and welded cans, but at the present time, the bonded cans and welded cans are more important.
Tin-plated, nickel-plated, chromium-plated steel strips as well as other metal strips can be used as the materials for three-piece can bodies. In most cases, the inner surface of the can body is formed by coating these materials with an organic coating (or a thermosetting coating) from the viewpoint of the storage properties of the contents (i.e., corrosion resistance), and the outer surface of the can body is printed with a label representing a content to be filled in the can.
The inner surface coating and outer surface printing are achieved by cutting the sheet-like steel material and then using three passes on a cut sheet coating line, a first pass for an inner surface coating, a second pass for an outer surface base coating and a third pass for an outer surface printing. Where a high degree of resistance to corrosion is required, the inner surface coating is carried out twice, and when a multi-color printing with five or more colors is used, the outer surface printing is carried out by printing twice, and consequently, the coating and printing of the inner and outer surfaces of the can body is carried out using four sheet passes or five sheet passes. It is necessary to heat the cut sheet in a baking oven at each pass.
Although the printing is desired to be effected continuously with the inner surface coating and the outer surface base coating by a coil coating method, it is difficult to achieve this continuous printing economically and accuracy.
The technique of laminating film onto a steel strip is old and has been well investigated in the past in the field of cans. For example, as shown in Japanese Unexamined Patent Publication (Kokai) Nos. 62-227642 and 58-82717, the conventional technique has been applied principally to 5 gallon cans and two-piece can body known as DrD can body and DI can body, and to can lids, but there are no examples of the use of coil steel strips for three-piece can bodies having a bonded film on which an image of a label representing a content to be filled in the can has been printed as in the present invention.
As mentioned above, the three-piece can bodies used at present are manufactured via; a complicated coating and printing process, and the three-piece can body is essentially costly because of disadvantages such as (1) poor productivity, (2) long time required, (3) a large number of worker required, and (4) difficulty in improving the external appearance of the print finish, and these are factors which reduce competitiveness of the three-piece cans. Moreover, there is a demand in the market for a beautiful printed appearance with a high class image label, and a further improvement of the print quality on the outer surface of the can body is required.